The invention relates to a method for closing and opening a tapping hole of a metallurgical vessel, in particular a steelworks converter, in which method a closure body, which leaves clear an annular gap between the closure body and the wall of the tapping hole, can be moved out of a waiting position into a closure position, in which it covers the tapping hole, and back, and in which method, at least in the closure position, a pressurized gas is introduced into the tapping hole counter to the outflow direction of a molten material contained in the metallurgical vessel, and to a device for carrying out the method.
A method of this type and an arrangement for carrying out the method are known from DE 32 08 490 C and from AT 350 090 B.
In order for the molten steel to be tapped, oxygen-blowing steelworks converters have a dedicated tapping port which is arranged well below the converter mouth. When the converter is tilted into the tapping position, it is firstly slag which flows out of this tapping hole, known as first or flush slag, followed by steel, the vortex effect meaning that a certain quantity of slagxe2x80x94known as entrained slagxe2x80x94is carried with this steel, and finally, when there is no more steel in the converter, there follows bottoms slag until the converter is tilted back.
When pig iron is being refined to form steel, oxidation reactions result in undesirable accompanying elements from the molten iron which have an affinity for oxygen being bonded to oxygen, and the oxides formed are emitted in gas form or are transferred into the slag. After refining, a large number of elements for deoxidation and alloying purposes have to be added to the steel, and these elements have a higher affinity for oxygen then the undesirable accompanying elements which are trapped in the slag. Consequently, such alloying elements can reduce the undesirable accompanying elements from the slag, and themselves become part of the slag. Moreover, refining slags may be highly aggressive with regard to the refractory material of the melting vessel and casting ladle. Therefore, for quality reasons and for reasons of economy, it is desired to as far as possible prevent slag from being entrained during tapping and alloying of a molten material in the ladle.
That the slag be held back during the tapping operation from the oxygen-blowing steelworks converter isxe2x80x94as explained abovexe2x80x94a demand imposed on the metallurgist: the molten steel is tapped from the converter into the steel casting ladle via the tapping hole, and entrained slag floats on the molten steel in the ladle and has an adverse effect on the quality of the steel.
Methods and devices of the type described in the introduction have proven themselves in practice. The closure body leaves clear an annular gap with respect to the wall of the tapping hole, through which gap air is sucked into the interior of the metallurgical vessel by dint of the pressurized gas which is fed through the closure body and is blown into the tapping hole. As a result, the molten material inside the vessel is prevented from flowing out and the tapping hole is completely sealed by pneumatic means. A device of this nature is able to hold back approximately 50% of the total slag in the converter. 20% of the total slag flows out as first or flush slag. 30% of the total slag is formed by the entrained slagxe2x80x94known as the vortexxe2x80x94which runs out during tapping and cannot be influenced by any device.
The opening and closing of the tapping hole using one of the devices described above have proven useful in practice, but the following drawback does arise: with the known devices, the transition from slag discharge to steel discharge is monitored by means of a ratio pyrometer which, when the tapped material changes from steel to slag or from slag to steel, emits a pulse which is used to pivot the closure body inwards and outwards in order to close or open the tapping hole. The problem lies in the clarity of the signal. When a pressurized gas, such as for example nitrogen, is being blown in order to hold back slag, the tapping hole itself is blown clear. If steel then also reaches the inner opening of the tapping hole, it will penetrate into the tapping hole, since it is heavier. It is initially mixed with slag, resulting in an extremely turbulent state. However, the jet itself will initially still be held back by the pressurized gas. Consequently, above a certain bath level above the tapping hole, the increasing pressure of the molten steel will suddenly result in a reversal of this state, which is becoming ever more labile, until a rush of liquid steel pours into the tapping hole. The signal receiver will then respond, but it is impossible to prevent some of this quantity from pouring out before the closure body has been removed from the tapping hole. Steel is already flowing through the tapping hole onto the closure body before the tapping hole has been fully opened. The amount of steel which flows out is of the order of magnitude of 120 to 250 kg of steel, depending on the state of the tapping hole. This quantity pours over the closure device, thus imposing extremely high loads on the latter and causing skull formation.
Even if the pivoting movement of the closure body in the known devices is initiated as soon as the emergence of steel is detected, the closure body still moves a relatively long distance in the direction of the longitudinal axis of the tapping hole, so that even if the pivoting movement is carried out rapidly considerable skull formation on the closure body results. Only while there is no steel entrained with the jet flowing out of the tapping hole is there no risk of skull formation on the device, i.e. of material being deposited on the device. After it has cooled, solidified slag falls off relatively easily and scarcely inhibits the mobility of the device.
The invention aims to avoid the drawbacks and difficulties of the prior art and is based on the object of providing a method and a device for carrying out the method which significantly reduce the risk of skull formation and allow steel to be tapped off with a significantly reduced amount of slag running out.
According to the invention, this object is achieved, in a method of the type described in the introduction, by the fact that the closure body is moved out of the waiting position into the closure position and back with directions of movement which lie in different areas.
Preferably, the closure body, when it is being brought from the waiting position into the closure position, is firstly moved in a direction of movement which has a principal movement component which is approximately transverse with respect to the longitudinal axis of the tapping hole and, just before it reaches the closure position is moved in a direction of movement which has a principal movement component which is approximately in the direction of the longitudinal axis of the tapping hole, and when it is being moved out of the closure position into the waiting position is firstly moved a short distance in a direction of movement with a principal movement component which is approximately in the direction of the longitudinal axis of the tapping hole and is then moved a longer distance in a direction of movement with a principal movement component which is approximately transverse with respect to the direction of the longitudinal axis of the tapping hole. This makes it possible to reduce the movement of the closure body in the area of the jet emerging from the tapping hole to the absolute minimum required.
According to the prior art, to make it possible for a pressurized-gas jet to be introduced into the tapping hole so that ambient air is sucked in, the closure body is moved in a plane in which the longitudinal axis of the tapping hole lies, with the result that the closure body together with its pressurized-gas outlet comes to lie inside the tapping hole. As a result, the movement of the closure body in the area of the jet emerging from the tapping hole lasted a relatively long time, which according to the invention it is possible to avoid.
Expediently, the movement with the principal movement component which is approximately transverse with respect to the longitudinal axis of the tapping hole is implemented over a significantly longer distance than the movement with the principal movement component which is in the direction of the longitudinal axis of the tapping hole, preferably over a distance which is at least five to ten times as long.
A device for closing a tapping hole of a metallurgical vessel, in particular a steelworks converter, in which device a closure body can be brought out of a waiting position into a closure position, in which it covers the tapping hole, and back, leaving clear an annular gap between the closure body and the wall of the tapping hole, by means of a movement device, and in which device the closure body is provided with at least one pressurized-gas outlet, which is connected to a gas-supply line, on its side which, in the closure position, faces towards the tapping hole is characterized in that, with the movement device for bringing the closure body out of the waiting position into the closure position, the closure body can be moved firstly in a direction of movement with a principal movement component which is approximately transverse with respect to the longitudinal axis of the tapping hole and then into the closure position with a principal movement component which is approximately in the direction of the longitudinal axis of the tapping hole.
Preferably, two movement devices are provided, one of which enables the closure body to move with the principal movement component which is approximately transverse to the direction of the longitudinal axis of the tapping hole, and the further movement device enables the closure body to move with a principal movement component which is approximately in the direction of the longitudinal axis of the tapping hole, in which case, advantageously, the movement devices provided are two pivoting devices, the closure body being mounted on an arm which can pivot in two planes which are approximately at right angles to one another.
A device which is characterized in that the movement devices are formed by pressure-medium cylinders, which each act on the arm bearing the closure body by way of a system of levers, has proven particularly robust.
A preferred embodiment is characterized in that the closure body is arranged on an arm which projects from a pivot pin, which pivot pin is mounted pivotably on a rocker shaft which is directed approximately perpendicular thereto, the rocker shaft being mounted rotatably on a holding fixture arranged on the metallurgical vessel, in which case, advantageously, the rotary movement of the rocker shaft extends over approximately 40 to 60xc2x0, and the pivoting movement about the pivot pin extends over 5 to 15 xc2x0.
A structurally simple solution is characterized in that the pressure-medium cylinder for executing a rotation of the rocker shaft acts, via a lever acting on the rocker shaft, and the pressure-medium cylinder for executing the pivoting movement about the pivot pin acts, via a radially projecting rocker bearing on one end of an arm of an elbow lever, the other arm of which bears the closure body.